1. Field of the Invention
The present invention relates to a method and a system for processing composite image data.
2. Related Background Art
Typical conventional image data processing systems are divided between two types of systems, that is, processing systems for processing bi-level value image data such as a document, characters, and drawing data, and multi-level value image data processing systems for processing a halftone image (a multi-level value image) such as a photograph. The bi-level value image data processing system primarily aims at improvement of resolution rather than that of gradation expression, while the multi-level value image data processing system primarily aims at improvement of gradation expressions rather than that of resolutions.
When an image including characters and a photographic area is to be input to a conventional image processing system, gradation (or reproducibility of gray scale levels) of the photograph area is limited in the bi-level value image data processing system while a resolution of the character area is low in the multi-level value image data processing system.
Multi-level value image data can be expressed in a pseudo halftone mode by converting the same into bi-level value image data according to a dither method or a density pattern method. However, such a conventional technique has limitations, gradation and resolution are undesirably impaired, and a moire pattern is formed. In this manner, image degradation inevitably occurs.
Another conventional technique is also available to recognize character and halftone areas of document data and to reproduce only the halftone area in a pseudo-halftone mode. However, gradation and resolution are inevitably degraded.